Occupant restraint systems for use in vehicles are well known in the art. One such restraint system includes a crash sensor, an inflatable air bag, and an actuation circuit that controls deployment of the air bag in response to an output from the crash sensor. The crash sensor can be an accelerometer that provides an electrical signal having a value functionally related to the vehicle's deceleration. A controller evaluates the accelerometer signal and provides an actuation signal when it determines a vehicle crash condition is occurring of such nature that the air bag should be deployed. The actuation circuit includes a squib operatively connected to a source of inflation fluid.
In response to an actuation signal from the controller, the actuation circuit applies a current through the squib which causes the squib to ignite. When the squib ignites, the source of inflation fluid discharges gas into the air bag, which results in inflation of the air bag.
The art has recognized that it is not always desirable to inflate the air bag with 100% of the gas provided from the source of inflation fluid. One proposed system controls the amount of gas that inflates the air bag in response to the detected weight of the occupant. Such a system is disclosed in U.S. Pat. No. 5,232,243 to Blackburn et al. and assigned to the assignee of the present invention. Another proposed system, disclosed in Gentry et al., U.S. patent application Ser. No. 986,041, filed Dec. 4, 1992, now U.S. Pat. No. 5,330,226, and assigned to the assignee of the present invention, controls the amount of gas that inflates the air bag in response to detected occupant position.